The invention relates to a method for producing an assembly for an energy storage system and to an assembly of this type.
In the case of electrically operated vehicles, use is made of energy storage modules which each contain a plurality of individual battery cells combined to form a stack of battery cells. The stacks of battery cells are customarily braced in the manufacturing process by an encircling frame and retained in shape by the latter. The frame also serves for fastening the energy storage module to a housing or in a vehicle.
In order not to exceed a maximum operating temperature, a cooling apparatus is required, wherein use is frequently made of plate-like cooling elements through which a cooling fluid flows. It is known to combine one such cooling element in each case with an energy storage module to form an assembly. In order to transfer a sufficient amount of heat from the energy storage module to the cooling element, the energy storage module and the cooling element are pressed against each other in order to keep the contact surfaces in contact over as large an area as possible and thus to improve the transmission of heat. Air gaps between the energy storage module and the cooling element and unevennesses in the contact surfaces have a negative effect here on the transmission of heat.
In order to improve the transmission of heat, DE 10 2010 038 681 A1 describes arranging an elastic heat-conducting coating in the form of a film or an adhesive between the base of the energy storage module and a cooling arrangement in thermal contact with the latter. The coating compensates for unevennesses in the mutually adjacent components. The force necessary for the mutual pressing together is applied by spring elements which are arranged on a base of the cooling arrangement and which permanently produce a pressing force between the cooling arrangement and the energy storage module.
In the case of the known systems, tolerances can be compensated for only by deforming the individual components under the action of a pressing force which is as high as possible. The clamping means which are used and which hold the energy storage module and the cooling element together have to be of correspondingly stiff design and have to have a high degree of stability in order to be able to permanently apply the necessary high clamping forces.
It is an object of the invention to simplify the production of a unit consisting of energy storage module and cooling element and to design the resulting assembly to be more compact and more cost-effective.
This and other objects are achieved according to the invention by a method for producing an assembly for an energy supply system, wherein the assembly has an energy storage module and a plate-shaped cooling element. A deformable and adhesive heat-conducting layer is applied between a contact side of the energy storage module and a contact side of the cooling element. The energy storage module and the cooling element are subsequently pressed together, wherein the heat-conducting layer is used to produce a dimensionally stable adhesive connection between the energy storage module and the cooling element, which permanently connects the energy storage module to the cooling element. The adhesive connection here is so robust and dimensionally stable that no further measures have to be provided in order to connect the energy storage module and the cooling element to each other thermally and structurally mechanically permanently, i.e. over the service life of the assembly.
In a possible variant, the heat-conducting layer which is still deformable and adhesive during the pressing preferably hardens to form a dimensionally stable adhesive connection.
The energy storage module and the cooling element merely have to be pressed together until the adhesive connection has sufficiently hardened in order, for example, to be able to move the assembly. Additional mounting steps, for example inserting, centering and permanently holding down the individual components, are thereby also eliminated.
The cooling element is preferably a rigid, self-supporting cooling plate in which cooling ducts, in which a cooling fluid can flow, are provided. The cooling fluid may be a coolant or a refrigerant, depending on the cooling circuit used.
Since the adhesive connection between energy storage module and cooling element is designed to be dimensionally stable and self-supporting, an additional stiff, load-bearing clamping frame around the assembly can be dispensed with. For the further mounting, for example in a structure with further energy storage modules or in a vehicle, use may be made of the frame which is normally already present and with which the individual cells of the energy storage module are braced.
Preferably, an assembly consisting of an energy storage module and a cooling element is, in each case, installed in a mounting frame, said assemblies simply being exchangeable as a unit if the cooling element or the energy storage module is defective.
During the pressing, the energy storage module and the cooling element are pressed against each other with a predetermined pressing force for a predetermined pressing time, wherein it may suffice if the weight of the energy storage module acts on the deformable adhesive heat-conducting layer. However, use may also be made of suitable higher pressing forces, for example in order to improve the distribution of the adhesive or if adhesives which deploy their effect at a predetermined pressing force are used.
The deformable adhesive heat-conducting layer is preferably applied over the entire contact surfaces between energy storage module and cooling element in order to obtain a continuous, flat, heat-conducting connection which permits a uniform, high transmission of heat on the entire contact surface.
During the pressing, the heat-conducting layer compensates for surface unevennesses and fills the space between the contact side of the cooling element and the contact side of the energy storage module completely and without air gaps as far as possible such that heat can be uniformly transmitted over the entire contact surface between the energy storage module and the cooling element.
In a preferred embodiment, the heat-conducting layer contains a heat-conducting adhesive. The latter is intended to combine the properties therein of being deformable, adhesive, insulating against high voltage and readily heat-conducting. In addition, the heat-conducting adhesive is intended to be hardening in a dimensionally stable and load-bearing manner.
Instead of a heat-conducting adhesive, use can also be made of a heat-conducting casting compound. These terms are used synonymously here. The heat-conducting adhesive or the heat-conducting casting compound is preferably sufficiently fluid in order to flow around the manufacturing-induced unevennesses or tolerances on the contact sides of the energy storage module and of the cooling element. The heat-conducting casting compound can thus, for example, also creep into manufacturing-induced rounded portions or radii at the corners of the battery cells on the contact side of the energy storage module and can compensate for same. It is therefore also no longer necessary to design the contact side of the cooling element to be as flat as possible since production-induced unevennesses can be simply compensated for by the heat-conducting layer.
During the pressing, the reduction in the thickness of the heat-conducting layer is preferably limited, and therefore, after the pressing, the adhesive connection has at least one further second predetermined thickness. It is frequently advantageous to ensure for this purpose that, over the entire contact surface between energy storage module and cooling element, the surfaces of the two contacts do not come into direct contact with each other, but rather the entire transfer of heat always takes place via the adhesive connection in order to avoid local hot or cold zones and to prevent damage.
It is also possible, for example, to compensate for unevennesses in the contact sides of the energy storage module and/or the cooling element via the heat-conducting layer by first of all a layer of the heat-conducting adhesive being applied and preferably smoothed, said layer then being entirely or partially hardened before pressing.
In order to avoid air locks, the heat-conducting layer can be applied in paths and/or in a predetermined pattern, for example in a pattern of dots, stripes or zigzags, the pattern being configured in such a manner that, when the energy storage module and the cooling element are pressed onto each other, air is automatically pressed outward and therefore an adhesive connection is produced without air locks.
In a manner governed by the concept, the individual battery cells of the energy storage module are generally aligned via the electric connection terminal arranged along one side. By this means, the heat removal zone located on the opposite side of the respective battery cell is subject to tolerances which may provide for the contact side of the energy storage module not to be completely flat since the individual battery cells of the energy storage module are offset in relation to one another on this side because of the component tolerances. These and other component-induced tolerances should be able to be compensated for via the layer thickness of the applied deformable, adhesive and heat-conducting layer.
The thickness of the heat-conducting layer and of the adhesive connection can be selected to be of such a size that the adhesive connection also supplies high-voltage protection between the energy storage module and the cooling element if such protection is required as a consequence of the design of the battery cells and of the energy storage modules or the interconnection of the energy storage modules. The high-voltage protection can be entirely achieved here via a suitable heat-conducting adhesive or a suitable heat-conducting casting compound.
However, it is also possible to arrange a high-voltage protective film, in particular composed of a suitable plastic, for example PET, between the energy storage module and the cooling element.
The high-voltage protective film may also be part of the deformable and adhesive heat-conducting layer and may be used for producing the adhesive connection when the latter is designed to be adhesive on one side or two sides. When a high-voltage protective film which is adhesive on two sides is used, it is optionally possible entirely to omit an additional heat-conducting adhesive and to realize the heat-conducting layer exclusively via the high-voltage protective film. A previous alignment of the cells of the energy storage module on the heat-removing zone of the cells is advantageous here because of the low tolerance-compensating capability of the high-voltage film. High-voltage protective films which are adhesive on one side are preferably used together with a layer of a heat-conducting adhesive.
In a preferred variant of the method, a high-voltage protective film is applied to the contact side of the energy storage module or of the cooling element. A heat-conducting adhesive is applied to the high-voltage protective film, to the cooling element and/or to the energy storage module. The energy storage module is subsequently pressed together with the cooling element before the heat-conducting adhesive hardens, in order to produce the adhesive connection. When a high-voltage protective film which is adhesive on one side is used, the respective surface facing the adhesive side of the high-voltage film is intended to remain free from heat-conducting adhesive.
The contact side of the cooling element and/or of the energy storage module is preferably cleaned beforehand in order to remove dirt particles, to improve the adhesion and thereby to prevent possible air locks.
After the high-voltage protective film has been adhesively bonded on, it is advantageous to clean and/or to activate the surface thereof in order to reduce air locks and to produce a better connection to the heat-conducting adhesive. The cleaning takes place, for example, with cleaning agents or solvents which remove contaminations of a chemical and mechanical type. For the activation, it is possible, for example, to perform a plasma treatment which improves the adhesion of an adhesive. Cleaning is also obtained here at the same time. The activation is preferably carried out after the film is adhesively bonded on and before the heat-conducting adhesive is applied to the film.
In order to position cooling element and energy storage module as accurately as possible in order to produce the adhesive connection, the cooling element can be placed into a pressing apparatus and fixed therein in a predetermined position via a positioning device. The positioning device can have, in particular, a supporting surface which corresponds to a negative shape of that surface of the cooling element which rests thereon. This is advantageous especially if that surface of the cooling element which lies opposite the contact side has, for example, a pattern of ribs for stiffening purposes, or if flow ducts are defined there in the interior of the cooling element such that said surface of the cooling element is not flat. By means of the provision of a negative to the geometry of the surface of the cooling element, the contact surface between centering apparatus and cooling element is maximized, and therefore forces are distributed uniformly during the pressing and inadvertent deformation of the cooling element is counteracted.
A positioning device is preferably also provided for the energy storage module, via which the latter is brought into the desired position thereof with respect to the cooling element. After the heat-conducting layer has been applied, the cooling element has been positioned and the energy storage module has been positioned, the pressing then takes place in order to produce the adhesive connection.
The object of the invention is also achieved by an assembly having an energy storage module and a plate-shaped cooling element, which assembly can be produced according to one of the above-described methods. A contact side of the energy storage module is bonded in a flat, integrally bonded, permanent and dimensionally stable manner to a contact side of the cooling element such that the energy storage module and the cooling element form a structural unit. Further clamping forces for optimizing the transfer of heat between said two components, as described above, are not required.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.